I am interested in finding the approximate serial number ranges of the 1921 Colt different pattern receiver markings. For Instance what approximate serial numbers utilized the 1st pattern(41-?), 2nd(?-?), 3rd(?-?), and 4th(?-15xxx)? Just trying to research what percentage of numbers used each of the different four "1921" configurations. If anyone has pictures of the patterns I will be most grateful. Were the Colt frames serialized at all?It appears that the Colt frames did not have the center ridge running down the area where the pistol grip attaches as compared to the Savage and AOC manufactured frames. Is that a correct assumption?

Sorry for all of the questions but I have been doing research on the Colt weapons and am looking for some accurate info and I always appreciate all of your combined knowledge. Thank You all in advance, Brent

Not sure what you mean by "different pattern" receiver markings? If you mean the "semi automatic, automatic" markings on the frame vs "full auto, semi auto" markings I can understand the question. If you want to know which of the 15,040 serial numbers belong to the individual type 1921 AC, 1921A, 1927or 1928N's, there isn't any range. All of the four types run the gambit of ranges.

There are three types of Markings for Colt '21 Receivers. '21 Early, '21 Middle, and '21 late. As far as Serial Numbers in those ranges, I'm not 100% sure at the moment. I will have to take a look through a few things. Though there were design changes below the 3000 range. Such as, the Rounded Actuator Slot, rather than the Squared. Also, the Selector Markings are different. Guns below 3000 have Arrows pointing down for Fire & Safe. And "Automatic"-"Semi-Automatic" were changed to "Full Auto" and "Single". Yes, Colt '21 Frames have the Center Ridge. Indeed, the Frames were engraved with the same Serial Number as the Receiver. On the '21, the Serial Number were also stamped into the Grip Mount Slot. Guns with a Serial under 1000 also have the Number stamped into the ramp of the Barrel.

So above 3000 the Colt frames closely resembled the Savage left side frame markings for safety and selector?Were the Colt frame serial numbers in the same location of Savage and AOC under the buttstock slide?

When I am refering to the 4 patterns, Patten date difference, Thompson vs Auto-Ord marking in front of the sight, etc. Doug Richardson's catalog is the only piece of reference I can find at the time. I am not sure if the patterns fell into specific serial ranges? specific dates? or if the patterns even followed numerical order(1st -4th).

Is it also safe to say that Colt Receiver markings were stamped not rolled?Are there any pictures out there of the difference between the square or round actuator slot?

Depending on the Markings, (Early, Middle, Late) Patent dates do differ. Though I don't know what Serial Number Range falls into each group. Also, the Bullet Logo was changed too. The Serial Number was engraved on the bottom of the Frame, where the Buttstock Slides onto. Markings were Rolled, not stamped. The bottom of the Trigger Housings (Where you insert a Mag.) is more oval at the corners, than squared. There are several good books. "American Legend" by Tracie Hill, "The Thompson Submachine Gun" 1st and 2nd Edition by Hill, "Thompson Submachine Guns" by Bannan (LONG out of print), and "The Thompson Submachine Gun" by Cox. All these mentioned have good info on Colt '21 Guns. Franks Book, "American Thunder" has more to do with the Military Variations.

Now you guys are talking about the PATENT dates on the right side of the receiver? The latest date on Colt's under 14500 is December 28, 1920 and on Colt's above 14500 have January 17, 1922, February 14, 1922, and February 28, 1922. The "AUTO-ORD-CO" inside the bullet lgo is seen on Colt's below 5000. The rest have the "THOMPSON" thin bullet logo.

Colt, 1928/1928A1 Savage and 1928A1 Auto-Ordnance grip frames all have the serial number on the frame in the same location and have what you refer to as the "center ridge." The only difference is the serial number prefix for Savage guns "S" and Auto-Ordnance guns "A.O." All1921/1928 grip frames have the slotted rear grip.

The Savage made grip frames have the "Full Auto" markings on two lines exactly like the Colt grip frames. The 1928A1 Auto-Ordnance grip frames have the "Full Auto" markings on one line.

As far as the receivers, the previous posts are correct, there are really only three variations: (1) serial numbers below approx. 3000, squared actuator slot, automatic and semi-automatic selector markings and Aut-Ord-Co. logo on top; (2) rounded actuator slot, full-auto and single selector markings, Thompson bullet logo on top, (3) same as previous variation except additional Patent Dates after serial number range 14,500.

What is the fourth variation you are referring to? I am not familiar with any other Colt receiver variation. The serial number on all Colt guns was also in the area under the grip mount as Lionhart pointed out. Most, if not all 1928A1 Thompsons had the serial number stamped in the same three places as the original guns: the left side of the receiver, the grip frame and the recessed area under the grip mount.